U.S. patent application number 10/329980 was filed with the patent office on 2003-07-31 for information recording apparatus and method.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Kuwahara, Maho, Ogawa, Akihito, Watabe, Kazuo.
Application Number | 20030142606 10/329980 |
Document ID | / |
Family ID | 27603717 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030142606 |
Kind Code |
A1 |
Ogawa, Akihito ; et
al. |
July 31, 2003 |
Information recording apparatus and method
Abstract
An information recording apparatus varies an output level of
laser light according to the length of a segment in which
information is to be erased when information recorded on an
information recording medium is erased by use of laser light of a
preset output level.
Inventors: |
Ogawa, Akihito;
(Yokohama-shi, JP) ; Kuwahara, Maho; (Tokyo,
JP) ; Watabe, Kazuo; (Yokohama-shi, JP) |
Correspondence
Address: |
PILLSBURY WINTHROP, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
27603717 |
Appl. No.: |
10/329980 |
Filed: |
December 27, 2002 |
Current U.S.
Class: |
369/59.11 ;
G9B/7.028; G9B/7.099 |
Current CPC
Class: |
G11B 7/0062 20130101;
G11B 7/126 20130101 |
Class at
Publication: |
369/59.11 |
International
Class: |
G11B 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2001 |
JP |
2001-398176 |
Claims
What is claimed is:
1. An information recording apparatus comprising: a circuit which
varies an output level of laser light according to length of a
segment in which information is to be erased when information
recorded on an information recording medium is erased by use of
laser light of a preset output level.
2. An information recording apparatus comprising: a recording
section which is configured to record and erase information with
respect to an information recording medium by varying an output
level of laser light, and a control section which is configured to
variably change an output level used to erase information with
respect to said recording section according to length of a segment
in which information is to be erased.
3. An information recording apparatus according to claim 2, wherein
said control section has at least two output levels used to erase
information and selectively switches the output levels according to
the length of a segment in which information is to be erased.
4. An information recording apparatus according to claim 2, wherein
said control section sets the output level of laser light at a
first level when the length of the segment in which information is
to be erased is equal to a first length and sets the output level
of laser light at a second level which is different from the first
level when the length of the segment in which information is to be
erased is equal to a second length which is different from the
first length.
5. An information recording apparatus according to claim 2, wherein
said control section includes a detection section which is
configured to detect a segment in which information is to be
erased, and a setting section which is configured to set the output
level of laser light at a first level when the length of a segment
detected by said detection section is equal to a first length and
set the output level of laser light at a second level which is
different from the first level when the length of the segment
detected by said detection section is equal to a second length
which is different form the first length.
6. An information recording apparatus according to claim 4, wherein
said control section sets the first level lower than the second
level when the first length is smaller than the second length.
7. An information recording apparatus according to claim 6, wherein
the first length contains minimum channel length of information to
be recorded on the information recording medium.
8. An information recording apparatus according to claim 2, wherein
said control section adds currents by selectively combining output
currents of a plurality of constant current sources according to
the length of a segment in which information is to be erased and
selectively switches the output level used to erase
information.
9. An information recording apparatus according to claim 2, wherein
said control section selects one of output currents of a preset
number of constant current sources according to the length of a
segment in which information is to be erased and selectively
switches the output level used to erase information.
10. An information recording apparatus according to claim 2,
wherein said recording section can selectively set the output level
of laser light to peak power to heat the information recording
medium to a temperature higher than a melting point thereof and
melt the same, erase power to hold the temperature of the
information recording medium at a crystallization temperature for a
crystallization holding time, and bias power to rapidly cool the
melted information recording medium and convert the same into an
amorphous form.
11. An information recording apparatus according to claim 2,
wherein said recording section forms recording marks formed in the
amorphous form and spaces which are crystallized portions on the
information recording medium in an array corresponding to
information to be recorded.
12. An information recording method comprising: recording and
erasing information with respect to an information recording medium
by changing output levels of laser light, and varying an output
level used to erase information according to length of a segment in
which information is to be erased.
13. An information recording method according to claim 12, wherein
varying the output level includes detection of a segment in which
information is to be erased, and setting the output level of laser
light at a first level when the length of a detected segment is
equal to a first length and setting the output level of laser light
at a second level which is different from the first level when the
length of the detected segment is equal to a second length which is
different form the first length.
14. An information recording method according to claim 13, wherein
the first level is set to be lower than the second level when the
first length is smaller than the second length.
15. An information recording method according to claim 14, wherein
the first length contains a minimum channel length of information
to be recorded on the information recording medium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2001-398176, filed Dec. 27, 2001, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to an information recording apparatus
and method for recording information on an information recording
medium. Particularly, this invention can be effectively used to
record information on a thermal recording type information
recording medium and erase recorded information.
[0004] For example, as information recording mediums, there is
DVD-RAM (Digital Versatile Disk Random Access Memory), DVD-RW
(Rewritable), DVD-R (Recordable), CD-RW (Compact Disk), CD-R and
the like.
[0005] 2. Description of the Related Art
[0006] As is well known in the art, as a recordable and rewritable
information recording medium, a thermal recording type information
recording medium is provided, in which information is recorded by
heating and cooling the information recording medium.
[0007] A typical example of a thermal recording type information
recording medium is a phase change medium. A phase change medium
records information based on a difference in the phase thereof,
that is, a difference in the physical property between an amorphous
state and crystalline state.
[0008] That is, there is a difference in the light reflection
factor between the amorphous state and crystalline state.
Therefore, it becomes possible to record information by arranging
portions which are formed in an amorphous form and portions which
are formed in a crystalline form along a track according to
information to be recorded.
[0009] For example, in an optical disk apparatus using the phase
change medium, the entire surface of the medium is previously
crystallized by the initialization process. Then, amorphous
recording marks are formed on the medium by applying an intense,
pulsed laser light thereto.
[0010] This is because the crystallized portion is melted by
application of the strong laser light, and then, the melted portion
is rapidly cooled when the laser light applied thereto becomes weak
and is converted into an amorphous form. The portion in the
amorphous form is called a recording mark. As a result, the
recording marks and spaces which are the crystallized portions are
arranged along the track.
[0011] When information is reproduced, a weak laser light of a
constant level is applied to the medium to read out recorded
information by converting changes in the amount of light reflected
from the amorphous-form portions that are the recording marks, and
the crystallized portions, into an electrical signal.
[0012] As the phase change medium which is recently put into
practice, there is provided a DVD-RAM [ISO (International
Organization for Standardization)/IEC (International
Electrotechnical Commission) 16824].
[0013] When information is recorded, the output level of laser
light is cyclically controlled for a segment in which recording
marks are to be formed so as to convert corresponding portions into
an amorphous form by melting and rapidly cooling the medium.
Further, the bias power which maintains the crystallized form is
applied to a space between the recording marks.
[0014] That is, information is recorded or erased based on
variation in the output level of laser light applied to the medium.
The recording waveform obtained at this time is generally called a
write strategy.
[0015] The write strategy is defined for each shape (pattern) of a
recording mark to be formed. In the write strategy of DVD-RAM,
three or four levels are provided as light outputs.
[0016] The light outputs include the peak power used to melt the
phase change medium by heating the same to a temperature equal to
or higher than the melting point thereof, the bias power (erase
power) used to hold the temperature of the medium at the
crystallization temperature for crystallization holding time, and
the bias power (multi-bottom power) and bias power (off-pulse
power) used to rapidly cool the melted medium and convert the same
into an amorphous form.
[0017] In a DVD-RAM, the size and shape of a recording mark are
adjusted with high precision by adjusting the above output levels
of laser light.
[0018] Further, for DVD-RAM, each output level of laser light
defined by the write strategy is made constant irrespective of the
length of the recording mark and space. When a long recording mark
is recorded, the number of cycles is increased, and when a short
recording mark is recorded, the number of cycles is decreased.
[0019] Spaces are provided before and after the recording mark. The
length of the space and the length of the recording mark correspond
to the recording pulse waveform.
[0020] If a short space is provided immediately before or after the
recording mark, heat used to form the recording mark may be
transmitted to the space and melt it. This means that the space of
a precise length cannot be formed, in other words, the precise
shape of the recoding mark cannot be attained.
[0021] Further, if a short recording mark is formed immediately
after a long space, the power of laser light is maintained at a
bias power (erase power) in which the period of the space is
constant, then changed to peak power used to melt the medium in a
short period of time, then changed to bias power (off-pulse power)
used to rapidly cool the melted medium and convert it into an
amorphous form. As a result, the amount of heat at the time of
formation of the space influences the recording mark forming
portion, and sometimes the head portion of the recording mark is
not formed in the precise position.
[0022] Jpn. Pat. Appln. KOKAI Publication Nos. 4-265522 and
11-102522 propose techniques for overcoming the above problem. An
outline of the technique disclosed in Jpn. Pat. Appln. KOKAI
Publication No. 4-265522 follows.
[0023] Attention is paid to mutual thermal interference occurring
in the array of the recording mark, space, recording mark, space, .
. . In order to suppress the thermal interference, the application
energy in the leading edge and trailing edge of a laser light pulse
is controlled to enhance the precision of formation of a recording
mark.
[0024] That is, in the recording portion, a pulse (which is
referred to as an off pulse) of power weaker than the erase power
is added to not only the last portion of the light pulse but also
the staring portion thereof. As a result, heat used to form the
present recording mark can be prevented from being transmitted to a
recording mark formed immediately thereafter, and heat used to form
the next recording mark can be prevented from being transmitted to
the previous recording mark. Further, since the power of the off
pulse is weaker than the erase power, the degree of rapid cooling
is significantly enhanced, enabling precise formation of recording
marks.
[0025] An outline of the technique disclosed in Jpn. Pat. Appln.
KOKAI Publication No. 11-102522 follows. In this publication also,
attention is paid to mutual thermal interference occurring in the
array of the recording mark, space, recording mark, space, . . .
That is, the widths of the recording marks and spaces are detected
and the light output level is changed according to a pattern
indicating portions in which significantly strong thermal
interference occurs.
[0026] However, the above methods have some problems. For example,
in the above-described DVD-RAM, the problem of thermal interference
cannot be sufficiently solved by use of the method for changing
only the pulse width for each pattern of the recording marks and
spaces or the length of the recording mark and space.
[0027] Further, in Jpn. Pat. Appln. KOKAI Publication No. 4-265522,
an attempt is made to prevent thermal interference by arranging the
off pulses before and after the recording pulse. However, there
still occurs a problem that a recording mark formed by the rapid
cooling effect of the off pulse may be re-crystallized by the erase
power used after this, for example.
[0028] If the off pulse is made excessively long, the time required
for switching circuits to output the next peak power cannot be
attained and it becomes difficult to control the pulse.
[0029] Further, in Jpn. Pat. Appln. KOKAI Publication No.
11-102522, a method for increasing the recording peak power only
for a recording mark immediately after the shortest space or the
shortest mark in which significantly strong thermal interference
occurs or applying an off pulse immediately before the peak power
is proposed.
[0030] However, in the high-density recording operation, heat
caused by application of pulses to form recording marks before and
after recording marks surrounded by the shortest spaces leaks into
the recording mark. Further, if the peak power is increased, the
medium may be melted, but it cannot be rapidly cooled and there
therefore occurs a problem that an amorphous recording mark cannot
be formed with high precision.
[0031] In all of the above-described conventional techniques,
attention is paid to the light pulse used to form recording marks.
However, in the rewritable type optical disk, it is necessary to
overwrite or erase the recording marks which have been already
recorded, at the time of recording of new information. In the
high-density recording operation, a problem occurs at the erase
time of information.
[0032] That is, at the erase time of information, it is necessary
to hold the temperature of the medium at the crystallization
temperature for crystallization holding time. Therefore, the write
strategy is made to set the erase power of laser light in a potion
in which no recording mark is formed. The erase power is optimized
to power which can hold the temperature of the medium at the
crystallization temperature.
[0033] However, in the high-density recording operation, not only
the recording mark but also the space between the recording marks
is made shorter. In the case of such a short space, even if the
erase power is output like the case of a long space, the heat
amount of peak power to record recording marks immediately before
and after the space leaks into the space portion, thus the
temperature of the medium rises above the ideal temperature.
[0034] As a result, in the short space, the temperature of the
medium exceeds the crystallization temperature and the space
portion is melted, thus the recording mark cannot be erased.
Further, even when the erase power is set at an intermediate point
between the optimum point in the case of the short space and the
optimum point in the case of the long space, a margin of the erase
power cannot be obtained.
BRIEF SUMMARY OF THE INVENTION
[0035] The present invention has been made in view of the above
conditions and an object thereof is to provide an information
recording apparatus and information recording method which can
precisely form recording marks, reduce the load on a recording
circuit and significantly improve the erase characteristic at the
rewriting time and the erase power margin by utilizing plural types
of erase powers.
[0036] According to one aspect of the present invention, there is
provided an information recording apparatus comprising a circuit
which changes an output level of laser light according to the
length of a segment in which information is to be erased when
information recorded on an information recording medium is erased
by use of laser light of a preset output level.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0037] FIGS. 1A and 1B are diagrams showing a recording pattern and
recording waveform, for illustrating one embodiment of the present
invention,
[0038] FIG. 2 is a characteristic diagram for illustrating the
relation between the erase rate and erase power corresponding to
the recording waveform in the above embodiment,
[0039] FIGS. 3A and 3B are diagrams for illustrating variations in
recording marks when overwriting occurs in the above
embodiment,
[0040] FIG. 4 is a block diagram for illustrating an information
recording/reproduction apparatus in the above embodiment,
[0041] FIGS. 5A to 5G are timing diagrams for illustrating the
recording operation of the information recording/reproduction
apparatus of the above embodiment,
[0042] FIG. 6 is a block diagram for illustrating a semiconductor
laser unit of the above embodiment in detail,
[0043] FIGS. 7A to 7F are timing diagrams for illustrating another
recording operation of the information recording/reproduction
apparatus of the above embodiment,
[0044] FIGS. 8A and 8B are timing diagrams for illustrating a
recording operation in comparison with the operation shown in the
timing diagrams of FIGS. 7A to 7F,
[0045] FIGS. 9A to 9E are timing diagrams for illustrating still
another recording operation of the information
recording/reproduction apparatus of the above embodiment, and
[0046] FIGS. 10A to 10F are timing diagrams for illustrating
another recording operation of the information
recording/reproduction apparatus of the above embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0047] There will now be described embodiments of this invention
with reference to the accompanying drawings.
[0048] (Recording Strategy)
[0049] FIG. 1A shows part of a recording pattern of (1,7) RLL (Run
Length Limited) modulation explained in the present embodiment and
FIG. 1B shows a recording waveform corresponding to the recording
pattern, that is, write strategy. The write strategy is roughly
divided into recording periods or recording portions and erase
periods or erase portions. In the following description, they are
respectively explained as recording portions and erase
portions.
[0050] FIG. 1B shows erase portions E1, E2, E3 and recoding potions
R1, R2, R3 and a recording waveform of laser light corresponding to
the above recording pattern. The maximum power of the laser light
used to melt the medium is set at peak power PP in the recording
potion and the initial power thereof used to cool the melted medium
is set at bottom power PB.
[0051] Further, the laser light is controlled to be selectively set
at two bias powers P1, P2 (P2>P1) which are characteristic to
the present embodiment. The bias powers P1, P2 are used as erase
powers to convert the medium into a crystallized form.
[0052] In the erase portions E1, E2, E3, the output level of the
laser light is maintained at an erase power level as described
above. In the recoding potions R1, R2, R3, the laser light is
output in a multi-pulse form in which the light emission waveform
is divided in a plurality of short pulses so as to form the medium
into an amorphous form and form recording marks.
[0053] Each of the pulses configuring the multi-pulse is divided
into a first pulse 01, intermediate pulse 02 and last pulse 03
based on the function thereof. The first pulse 01 is a pulse to
heat the medium to a temperature higher than the melting point. The
intermediate pulse 02 is configured by a heating portion which
rises to the peak power PP and a cooling portion which falls to the
bottom power PB.
[0054] An increase in the size of the recording mark due to
excessive heating of the medium and a reduction in the size of the
recording mark due to melting and re-crystallization of the medium
can be suppressed by providing the cooling portion. Further, the
last pulse 03 is a heating pulse and used to shape the trailing
edge of the recording mark.
[0055] In the recording portions R1, R2, R3, the output levels of
the laser lights caused by the respective pulses 01 to 03 are
defined by the peak power PP and bottom power PB. In the erase
portions E1, E2, E3, the intensities of light are kept constant and
plural (two types in the present embodiment) intensities are
appropriately used according to the length of the spaces.
[0056] That is, when the space is shorter than the specified
length, the laser light is set to the bias power P1 as first erase
power EP1, and when the space is longer than the specified length,
the bias power P2 is set as second erase power EP2.
[0057] If light with the level of the bias power P1 or P2 is
applied to the medium, the medium is heated to the crystallization
temperature and held as it is at the crystallization temperature
for crystallization holding time. As a result, the medium is formed
into a crystallized form.
[0058] In the present embodiment, when 2T which is the shortest or
minimum channel length, is used as a threshold value, the bias
power P1 is assigned to the space of 2T and the bias power P2 is
assigned to the longer space (equal to or longer than 3T).
[0059] (Erase Power Margin)
[0060] FIG. 2 shows the dependency of "2T overwrite 7T erase rate
(2TO.W)" and "3T overwrite 7T erase rate (3TO.W)" on the erase
power in the high-density recording operation.
[0061] In this case, as shown in FIG. 3A, "2T overwrite 7T erase
rate" indicates a reduction amount of the amplitude of a reproduced
signal of a 7T mark-7T space pattern when a 2T mark-2T space
pattern is overwritten on the 7T mark-7T space pattern.
[0062] Further, as shown in FIG. 3B, "3T overwrite 7T erase rate"
indicates a reduction amount of the amplitude of a reproduced
signal of a 7T mark-7T space pattern when a 3T or more mark-3T or
more space pattern is overwritten on the 7T mark-7T space pattern.
That is, the erase rate becomes so low that the 7T mark-7T space
pattern will disappear.
[0063] In conventional DVDs, a pattern of 3T to 11T as the space
length is used, but since any pattern has sufficient space length,
the characteristic of the erase rate will not be greatly influenced
by the length of the space.
[0064] On the other hand, in a high-density optical disk, the
minimum space length is made smaller. As a result, as indicated by
an erase portion S1 in FIG. 3A, when the space of the length which
is as short as 2T is used, a heat amount is increased by leakage of
heat from the recording power used for a recording mark which
exists immediately before or after the above 2T space. As a result,
the temperature of the medium exceeds the crystallization
temperature and the medium is sometimes melted.
[0065] In contrast, as indicated by an erase portion S2 shown in
FIG. 3B, when a long space is used, a heat amount is not
significantly increased even if leakage of heat is caused from the
surrounding portions into the space since application time of the
erase power is sufficiently long.
[0066] Therefore, when a signal containing a short space such as a
2T space is overwritten by use of an erase power which is optimized
for the length of a long space, the total erase rate is lowered in
comparison with a case wherein a signal containing only long spaces
is overwritten. That is, it is necessary to lower the optimum erase
power in a 2T space portion in comparison with a long space portion
by taking a leakage heat amount into consideration.
[0067] The result of the dependency on the erase power shown in
FIG. 2 also indicates the above fact. That is, in a case where the
2T pattern is overwritten, the highest erase rate is obtained when
the erase power is set at P2t. However, in a case where a pattern
of 3T or more is overwritten, the highest erase rate is obtained
when the erase power is set at P3t.
[0068] In this case, if a threshold value indicating the lower
limit of the erase rate is indicated by S, a power margin of P3tL
to P3tH can be attained for a pattern of 3T or more when the erase
power is set at P3t in the conventional recording waveform.
However, the erase power becomes lower than the threshold value S
in the case of a 2T pattern.
[0069] Likewise, even if the erase power is set at P2t, the erase
power becomes lower than the threshold value S in the case of a
pattern of 3T or more. If the erase power is set at an intermediate
value between P2t and P3t, the erase power can barely be set higher
than the threshold value S in either one of the above patterns.
However, since the erase power becomes lower than the threshold
value S if the erase power fluctuates only slightly, the erase
power margin M is extremely narrowed.
[0070] Therefore, in the present embodiment, as shown in FIG. 1B,
the bias powers P1 and P2 are respectively set to P2t and P3t. As a
result, the erase power becomes optimum for each space and it
becomes possible to precisely form recording marks.
[0071] Further, even when the light output varies, a sufficiently
large erase power margin M can be attained since the erase powers
are respectively set to different values for the 2T space and the
space of a different length.
[0072] (Recording Apparatus)
[0073] FIG. 4 shows an information recording/reproduction apparatus
which records/reproduces information with respect to the above
information recording medium. That is, an information reproduction
section 102 reads out information associated with the information
recording condition, information associated with addresses of an
information recording medium 101 and the like from the information
recording medium 101.
[0074] An address detection circuit 103 detects address information
of the information recording medium 101 based on the readout
information. The address information is read out by a CPU (Central
Processing Unit) 104. Thus, the CPU 104 recognizes the present
address of the information recording medium 101.
[0075] An input section 210 is supplied with user data to be
recorded. The user data is supplied to a recording pattern creation
circuit 211. The recording pattern creation circuit 211 creates a
signal having a recording pattern as shown in FIG. 1A based on the
input user data.
[0076] The signal is input to a recording pattern detection circuit
212. The recording pattern detection circuit 212 detects the
waveform of a recording pattern based on the input signal, creates
timing information of the rise or fall thereof and supplies the
same to a recording waveform control signal creation circuit
213.
[0077] The recording waveform control signal creation circuit 213
creates a recording waveform control signal so as to attain a
recording waveform as shown in FIG. 1B and supplies the recording
waveform control signal to a semiconductor laser driving circuit
214.
[0078] The operation of the semiconductor laser driving circuit 214
and the output timing of the recording waveform control signal from
the recording waveform control signal creation circuit 213 are
controlled by the CPU 104. That is, when user data is to be
recorded, it is necessary to record the data in a location
designated by an adequate address.
[0079] The semiconductor laser driving circuit 214 drives a
semiconductor laser unit 215 by use of a pulse train of a recording
waveform corresponding to the recording waveform control signal. As
a result, laser light output from the semiconductor laser unit 215
is applied to the information recording surface of the information
recording medium 101 via an optical system (not shown).
[0080] During the information recording operation, as explained
with reference FIG. 1B, the power of laser light is controlled to
be switched. The power switching information is created by the CPU
104 which recognizes the recording waveform control signal of the
recording waveform control signal creation circuit 213.
[0081] The power switching information is supplied from the CPU 104
to a light output setting circuit 216. The light output setting
circuit 216 controls the output level (intensity of the laser
light) of the semiconductor laser driving circuit 214 so that
powers of various levels explained in FIG. 1B can be obtained from
the semiconductor laser driving circuit 214 based on the input
power switching information.
[0082] In FIG. 4, the CPU 104 and the recording waveform control
signal creation circuit 213 are indicated as different blocks, but
they can be integrally formed as a system control section.
[0083] If the information recording medium 101 is an optical disk
and the information recording/reproduction apparatus is an optical
disk apparatus, for example, a spindle motor which rotates the
optical disk, an optical pickup which concentrates laser light on
the optical disk and the like are additionally used.
[0084] Further, in order to concentrate a laser light spot along
the recording track of the optical disk in an optimum state, a
focusing servo function, tracking servo function and the like are
additionally used.
[0085] When the information recording medium 101 is loaded on the
information recording/reproduction apparatus, it reads out
information associated with the information recording condition
from the information recording medium 101 by use of the information
reproduction section 102. Further, the information
recording/reproduction apparatus sets initial values of the light
output setting circuit 216, recording waveform control signal
creation circuit 213 and the like. Then, the information
recording/reproduction apparatus reads out address information of
the information recording medium 101 by use of the address
detection circuit 103.
[0086] If user data which is desired to be recorded is input to the
recording pattern creation circuit 211, the recording pattern
creation circuit 211 outputs a signal having a recording pattern as
shown in FIG. 1A. The recording pattern detection circuit 212 reads
out a recording pattern from the signal and outputs the readout
result to the recording waveform control signal creation circuit
213.
[0087] FIGS. 5A to 5G show examples of the signal waveforms of the
respective sections of the information recording/reproduction
apparatus. FIG. 5A shows a recording pattern. FIGS. 5B to 5E show
examples of the recording waveform control signal output from the
recording waveform control signal creation circuit 213. Further,
FIG. 5F shows the state of a variation in the power of laser light
output from the semiconductor laser unit 215.
[0088] In this example, a space shorter than the predetermined
specified length is detected by monitoring a recording pattern
(FIG. 5A) in addition to the operation of controlling the pulse
width used in the DVD-RAM, for example.
[0089] Then, in the short space segment, a recording waveform
control signal which permits the bias power P1 to be attained is
output. When the recording pattern is longer than the specified
length, a recording waveform control signal which permits the bias
power P2 to be attained is output. In the example shown in FIG. 5F,
a state in which the bias power P1 is set in a segment W1 and the
bias power P2 is set in a segment W2 is shown.
[0090] The semiconductor laser driving circuit 214 drives the
semiconductor laser contained in the semiconductor laser unit 215
based on the recording waveform control signal and the setting
value of the light output setting circuit 216 corresponding to the
recording waveform control signal. The output waveform of the
semiconductor laser driving circuit 214 is equivalent to that shown
in FIG. 5F. By the above operation, recording marks shown in FIG.
5G are formed on the information recording medium 101.
[0091] (Driving Method of LD (Laser Diode)) p FIG. 6 shows one
example of the semiconductor laser unit 215. A semiconductor laser
300 contained in the semiconductor laser unit 215 emits light in
response to a current output from a constant current source
310.
[0092] The constant current source 310 is configured by a plurality
of (in this example, four) parallel-connected constant current
circuits 301 to 304. An output current value of the constant
current source 310 is determined by the setting value of the light
output setting circuit 216.
[0093] Switching of the constant current circuits 301 to 304 to be
used is made by use of switching elements 311 to 314. The switching
elements 311 to 314 are respectively switched based on the
recording waveform control signals (FIGS. 5B to 5E) output from the
recording waveform control signal creation circuit 213 by use of
the semiconductor laser driving circuit 214.
[0094] In the case of a current adding type driving method, for
example, the output current value of the constant current circuit
301 is so set that laser light of the output level used for
reproduction, that is, laser light at a level of the bias power PB
can be output.
[0095] The output current value of the constant current circuit 302
is so set that the added current thereof with the output current of
the constant current circuit 301 will permit laser light at a level
of the bias power P1 to be output.
[0096] Further, the output current value of the constant current
circuit 303 is so set that the added current thereof with the
output currents of the constant current circuits 301, 302 will
permit laser light at a level of the bias power P2 to be
output.
[0097] Also, the output current value of the constant current
circuit 304 is so set that the added current thereof with the
output current of the constant current circuit 301 will permit
laser light at a level of the peak power PP to be output.
[0098] Then, the switching elements 311 to 314 are driven by the
semiconductor laser driving circuit 214 based on a combination of
logical values of the recording waveform control signals shown in
FIGS. 5B to 5E as explained before.
[0099] That is, when the recording waveform control signals shown
in FIGS. 5B to 5E are "1000", the semiconductor laser driving
circuit 214 turns ON only the switching element 311 so as to output
the bias power PB.
[0100] When the recording waveform control signals shown in FIGS.
5B to 5E are "1100", the semiconductor laser driving circuit 214
turns ON the switching elements 311, 312 so as to output the bias
power P1.
[0101] When the recording waveform control signals shown in FIGS.
5B to 5E are "1110", the semiconductor laser driving circuit 214
turns ON the switching elements 311, 312, 313 so as to output the
bias power P2.
[0102] When the recording waveform control signals shown in FIGS.
5B to 5E are "1001", the semiconductor laser driving circuit 214
turns ON the switching elements 311, 314 so as to output the peak
power PP.
[0103] The peak power PP corresponds to an output level of laser
light which is optimum to melt the information recording medium
101. The bias power PB corresponds to an output level of laser
light which is equivalent to that of reproduction power. The bias
power P2 corresponds to an output level of laser light which is
optimum to perform the erase operation for a long space, that is,
P3t shown in FIG. 2. The bias power P1 corresponds to an output
level of laser light which is optimum to perform the erase
operation for a short space, that is, P2t shown in FIG. 2.
[0104] When a signal of the recording pattern shown in FIG. 5A is
recorded by use of the recording waveform shown in FIG. 5F, the
rapid cooling effect can be attained so as to precisely record a 3T
recording mark even if a 2T space exists immediately after the 3T
recording mark, for example, since erase power specified by the
bias power P1 is sufficiently low.
[0105] In the 2T space portion, heat amounts used to record a 3T
recording mark and 4T recording mark lying before and after the 2T
space portion are transmitted thereto and the temperature of the
information recording medium 101 reaches the crystallization
temperature so that the recording mark can be overwritten and
erased.
[0106] Further, when a 3T space exists after a 4T recording mark,
the 4T recording mark can be precisely recorded since the space
length is large and thermal interference is weak. In the 3T space
portion, since optimum erase power specified by the bias power P2
is output, the recording mark can be overwritten and erased. Even
when the output levels fluctuates due to the temperature
characteristic of the circuit and the like, a sufficiently large
margin can be attained since the erase power is optimized according
to the space length.
[0107] Thus, by using the write strategy of the present embodiment,
a problem of the thermal interference in the high-density recording
operation can be solved, the erase characteristic can be improved
and the recording mark creation precision can be enhanced.
[0108] Further, the robust characteristic with respect to the erase
power can be enhanced. Also, since the rapid cooling effect can be
attained even if the off pulse is not used, the number of switching
operations of the output level of laser light can be reduced and
the control operation of the driving circuit can be performed at
high speed in a simple fashion.
[0109] In the present embodiment, one example of the current adding
type driving method is explained, but the same effect can be
achieved by using a different adding method if two types of power
levels can be provided for the erase power.
[0110] Further, when a current switching type driving method is
used, the output current value of the constant current circuit 301
is set so as to generate an output level of laser light for
reproduction, that is, bias power PB.
[0111] Further, the output current value of the constant current
circuit 302 is set so as to generate the bias power P1, the output
current value of the constant current circuit 303 is set so as to
generate the bias power P2, and the output current value of the
constant current circuit 304 is set so as to generate the peak
power PP. Then, the switching elements 311 to 214 are switched at
timings at which the output currents of the respective constant
current circuits 301 to 304 are output.
[0112] In the present embodiment, the bias power P1 is output in
the case of a 2T space and the bias power P2 is output in the case
of a space longer than the 2T space. However, it becomes necessary
to change the threshold value which is used to switch the bias
power depending on the degree of thermal interference. For example,
it is possible to output the bias power P1 in the case of a 2T
space and 3T space and output the bias power P2 in the case of a
space longer than the 3T space.
[0113] For example, if an EFM (Eight to Fourteen Modulation) system
or the like is used as the modulation system, it is possible to
output the bias power P2 in the case of a 3T space and output the
bias power P1 in the case of a space longer than the 3T space.
[0114] Further, as a laser light source used for recording, not
only the semiconductor laser but also a gas laser or solid-state
laser can be used, and in this case, the same effect as described
before can be attained. In addition, in the above-described
embodiment, a case wherein two levels of erase power are used is
explained, but it is of course possible to use a larger number of
erase power levels.
[0115] FIGS. 7A to 7F shows another example of the write strategy
when an off pulse is used.
[0116] Like the conventional case, in the write strategy in which
only one erase power level is used, it is necessary to use a
relatively long off pulse (segments OFF1, OFF2) as in the write
strategy shown in FIG. 8B depending on the characteristic of the
information recording medium 101. In this case, FIG. 8A shows a
recording pattern and FIG. 8B shows the recording waveform of laser
light.
[0117] However, if the above write strategy is used, an output of
peak power appears directly after the off pulse and there occurs a
problem that it is difficult to drive the semiconductor laser.
[0118] In addition, there occurs a problem that the erase operation
cannot be adequately performed since the off pulse is long, and the
recording mark formed by the rapid cooling effect due to the off
pulse will be shrunk by leakage of erase power which is generated
after this process.
[0119] Therefore, in the write strategy of the present embodiment,
the erase power of two levels is used in addition to the off pulse
to solve the above problem.
[0120] That is, the length of the off pulse can be reduced and the
recording mark can be prevented from being shrunk after the end of
the off pulse by setting the erase power to the level of the bias
power P1 for a space which causes strong thermal interference, that
is, a short space so as to reduce the thermal interference.
[0121] Further, the satisfactory erase rate can be attained by
setting the erase power to the level of the bias power P2 for a
long space which causes weak thermal interference.
[0122] The present invention is not limited to the above
embodiment. For example, when the present invention is applied to
the write strategy in which the multi-bottom is not utilized as
shown in FIGS. 9A to 9E or to the write strategy in which the pulse
is not divided into small portions as shown in FIGS. 10A to 10F,
the effects thereof can be securely attained.
[0123] FIG. 9A shows a recording pattern, FIGS. 9B to 9D show
recording waveform control signals and FIG. 9E shows a recording
waveform. In the recording waveform, bias power P3 is set. In
comparison with the recording waveform shown in FIG. 7F, the bottom
power PB used to perform the cooling operation is not provided and
the power level used to perform the cooling operation is set at the
level of the bias power P1.
[0124] FIG. 10A shows a recording pattern, FIGS. 10B to 10E show
recording waveform control signals and FIG. 10F shows a recording
waveform. In the recording waveform, a power level P4 is set
immediately after the peak power PP. In this example, the power
level P4 is given at a timing at which the information recoding
medium 101 is melted to attain the amorphous state.
[0125] In the above embodiment, when laser light is applied to the
information recoding medium 101 to record information thereon, the
laser light is divided into pulses at a plurality of output levels
and controlled to record and erase information by selectively
switching the output levels.
[0126] In this case, one of the output levels which corresponds to
the information erase power has at least first and second levels,
the first level is used when the length of a to-be-erased portion
is a first length and the second level is used when the length of a
to-be-erased portion is a second length.
[0127] If the length of the to-be-erased potion becomes different,
the erase characteristic and the formation precision of a recording
mark are deteriorated due to a difference in the degree of thermal
interference in some cases. Further, if the length of the
to-be-erased potion becomes different, the optimum erase level will
be different.
[0128] Therefore, in the above embodiment, the erase characteristic
and the formation precision of a recording mark can be enhanced and
the robust characteristic of the erase level can be enhanced by
using at least two types of erase levels and selecting the optimum
power level according to the length (segment) of a portion to be
erased.
[0129] Further, in the present embodiment, the first length is the
minimum channel length in the modulation rule used when information
is recorded and the second length is the other channel length.
Since the degree of thermal interference is greatly different
between the length of a to-be-erased portion with the minimum
channel length and the other lengths, the erase characteristic can
be more effectively enhanced by separately setting the conditions
according to the lengths.
[0130] Also, in the present embodiment, when the first length is
shorter than the second length, the first level is set at a level
lower than the second level. In a case where a potion of the
minimum channel length is erased, a leakage heat amount occurring
when recording marks lying before and after the above portion are
formed is larger than that occurring in a case where a portion of
the other channel length is erased.
[0131] Therefore, it becomes possible to attain a balance between
the erase levels when leakage of the heat amount occurs by setting
the erase level used to erase a portion of the minimum channel
length lower than the erase level used to erase a portion of the
other channel length. As a result, it becomes possible to enhance
the erase characteristic and the formation precision of a recording
mark.
* * * * *